Alright, how do I take a screenshot with my Macbook?
Does this work?
Anyway, it seems the problem only occurs over wireless. But when I try at home with ethernet cable, it works. What might be the reason for this?
Is reager.no your ISP at your house? It could be that your ISP does not allow smtp access from outside it's own network. I know that I cannot connect to my ISP's smtp server when I am not at home.
You said you had some windows machines that worked fine - do they work on the same wireless networks that the mac fails on?
Yes, you need to test telnet to your SMTP connection under the same conditions as when Mail doesn't work.
Is this summary correct?
You can mail from a Windows machine via wired ethernet at home
You cannot connect from a wireless connection using your Mac outside your home
Does Mail work from your Mac at home?
Does Windows work outside your home?
Have you tried another mail client like Thunderbird on your Mac?
I have the glimmering of a suspicion that your SMTP server only accepts connections from a single IP address.